If I understand you post correctly you are leaving the ski in the salt water when not in use, not on a trailer, right? If so you won't be able to flush the exhaust and intercooler. Also it doesn't take long for the hull to foul in warm salt water....I wouldn't do this with my ski's....
We had a similar problem and changed the ring but also the impeller was bent a little and had to repitch , ran fine afterwards. Check your prop closely
I fill both our '19 and'18 RXTX with 93 than if I need to add fuel at the marina I feel it should still be close to 91. Also we just bought two Link fuel caddies...